1. Field of the Invention
The present invention relates to a liquid supplying method for supplying ink used for image formation on a recording medium or for supplying processing liquid used for adjusting the printing quality of ink to be discharged onto a printing medium.
2. Description of the Related Art
An example of a typical inkjet printer that forms an image by discharging ink is a serial-scanning type. An inkjet printer of this type is provided with a cartridge that includes an ink-discharging print head and an ink tank that are detachably combined with each other. Such a cartridge is disposed on a carriage. By driving the carriage in a main scanning direction and feeding printing paper in a sub scanning direction, the inkjet printer performs a printing operation in a serial-scanning manner.
In an inkjet printer of a serial-scanning type, every time the ink in the ink tank becomes empty, the ink tank must be replaced with a new one. If the volume of the ink tank were to be increased in order to reduce the replacement frequency, the carriage becomes larger in size. This is problematic in view of louder noise and larger vibration during the printing operation.
Japanese Patent Laid-Open No. 8-323996 (corresponding to U.S. Pat. No. 5,280,300), for example, discloses a structure for preventing such problems. In detail, a relatively small sub tank is provided on a carriage, and a larger-sized main tank is also provided such that the main tank is connected to the sub tank via a tube and a valve. When the ink in the sub tank decreases and the negative pressure in the sub tank thus increases, the valve is opened so that the sub tank communicates with the main tank. The difference in pressure between the sub tank and the main tank allows the ink contained in the main tank to be supplied to the sub tank.
According to Japanese Patent Laid-Open No. 8-323996, however, the sub tank and the main tank must be positioned vertically with respect to each other, and therefore, an overall size reduction of a printer is difficult. Moreover, a driving source for an ink-supply operation is defined by a negative-pressure generating mechanism provided inside the sub tank, and a driving force that can be generated by the negative-pressure generating mechanism is limited to an extent that discharge nozzles can be maintained in a proper condition. As a result, the ink-supply operation takes a large amount of time. On the other hand, as a type of method for supplying the sub tank with ink contained in the main tank, an intermittent ink-supplying method, which will be referred to as a pit-stop ink-supplying method hereinafter, is known. In the pit-stop ink-supplying method, the main tank and the sub tank are disconnected with each other during a printing operation, and are connected to each other when the sub tank needs to be supplied with ink. If such method type is applied to the structure disclosed in Japanese Patent Laid-Open No. 8-323996, the printing operation has to pause for a long period of time if the ink-supply operation takes a large amount of time. Furthermore, if the printer is tilted at an angle, there may be cases where, for example, the ink cannot be supplied to the sub tank depending on the angle, or the ink may leak through the nozzles due to oversupplying of ink.